Mutsus are little pets that swim in a tank...it requires water. There are turtles..dogs..bunnys..fishes..and penguins. You can choose one animal and then the Mutsu comes with the tank for it to swim into. There are 3 buttons on the tank, and you also get a control to feed it and all that stuff! IT's soooo cool, it's like a REAL pet fish..it's actually real...all the stuff you really do for a fish and the coolest thing about it is the WATER part!